Chapter 7 Section 3 Movement through the membrane

Key Concept: How does active transport differ from diffusion?

Active transport requires the input of energy, but diffusion does not require additional energy.

Key Concept: What happens during diffusion?

Diffusion causes many substances to move across a cell membrane but does not require the cell to use energy.

Key Concept: How does diffusion affect cells?

Diffusion causes many substances to move across a cell membrane without the cell's using energy.

Key Concept: What are the main functions of the cell membrane?

The cell membrane regulates what enters and leaves the cell and also provides protection and support. The cell takes in food and water and eliminates wastes through the cell membrane.

Key Concept: What is the basic structure of a cell membrane?

The core of nearly all cell membranes is a double-layered sheet called a lipid bilayer. Most cell membranes contain protein molecules that run through the lipid bilayer, and carbohydrate molecules are attached to these proteins. There are so many colecules attached to the membrane that scientists call the membrane a mosaic of molecules.

Key Concept: Describe how water moves during osmosis.

Water tends to diffuse from a region where it is highly concentrated to one wher it is less concentrated. Water will move across a membrane until equilibrium is reached.

osmosis

diffusion of water through a selectively permeable membrane

lipid bilayer

double-layered sheet that forms the core of nearly all cell membranes

active transport

energy-requiring process that moves material across a cell membrane against a concentration difference

facilitated diffusion

movement of specific molecules across cell membranes through protein channels

exocytosis

process by which a cell releases large amounts of materials

endocytosis

process by which a cell takes material into the cell by infolding of the cell membrane

diffusion

process by which molecules tend to move from an area where they are more concentrated to an area where they are less concentrated

phagocytosis

process in which extensions of cytoplasm surround and engulf large particles and take them into the cell

selective permeability

property of biological membranes that allows only certain substances to pass through them

concentration

the mass of solute in a given volume of solution, or mass/volume